Liver toxicity is the leading cause of pre-launch and post-market attrition of pharmaceutical compounds (i.e. Rezulin, Prexige). Significant species-specific differences in organ functions now necessitate supplementation of animal data with assays designed to assess human responses to drugs. Adherent cultures of primary human hepatocytes are considered to be the gold standard for evaluating preclinical drug metabolism, enzyme induction, and liver-specific toxicity. However, hepatocytes display a rapid (hours) decline in liver-specific functions under conventional culture conditions utilized routinely for drug development. Recently, a robust model of human liver tissue has been developed with optimized microscale architecture in an industry-standard multiwell format that retains liver-specific functions for 4-6 weeks in vitro. Hepatocytes in this microscale platform secrete liver-specific products, display functional CYP450 and conjugation enzymes, secrete molecules into the bile canaliculi, and maintain high levels of expression of liver-specific genes relevant for evaluating drug disposition. The primary objective of this Small Business Innovation Research (SBIR) Phase II project is to further develop and optimize these microscale human liver cultures and couple them with miniaturization strategies and assay technologies for cost-effective high-throughput in vitro screening. Since drug-induced liver injury (DILI) is a leading cause of acute liver failures and the high attrition rate of pharmaceuticals, we will optimize our miniaturized human livers specifically for the in vitro screening of genotype-specific and clinically-relevant drug disposition and coupled DILI. The technologies we develop here may find broad utility in the development of several classes of therapeutic compounds (drugs, biologics), in evaluating the disposition and injury potential of environmental toxicants, in fundamental investigations of liver physiology and disease, in the identification of new biomarkers, and in personalized medicine for liver disease. In the future, continued combination of microtechnology with tissue engineering may spur the development of other tissue models and their integration into the so-called 'human-on-a-chip'. PUBLIC HEALTH RELEVANCE: The studies proposed in this project are aimed towards developing a miniaturized human liver microarray for high-throughput screening (HTS) applications, specifically for evaluating drug disposition and drug-induced liver injury, a serious challenge for patients, regulatory agencies and the pharmaceutical/biotech industry. In the future, our miniaturized micro-liver HTS system may eliminate problematic compounds much earlier in the drug development pipeline towards reducing patient exposure to unsafe drugs. The technologies we develop here may also find utility in assessing the injury potential of environmental toxicants, in basic research, and in personalized medicine for patients with liver disease.